1. Technical Field
The present disclosure relates to a slab amplifier, and a laser apparatus and an extreme ultraviolet (EUV) light generation apparatus including the slab amplifier.
2. Related Art
A lithography apparatus used to, for example, produce integrated circuits transfers a desired pattern on a substrate. In order to create a circuit pattern on the substrate, a patterning device referred to as “mask” or “reticle” is used. The pattern is transferred to the substrate by imaging the pattern on a radiation-sensitive material (resist) layer provided on the substrate (e.g. silicon wafer substrate).
The theoretically estimated CD (critical dimension) of the pattern transfer is given by the following equation (1).CD=k1·λ/NA  (1)
Here, λ represents the wavelength of exposure light used in the pattern transfer. NA represents the numerical aperture of a projection system used in the pattern transfer, k1 represents a process-dependent coefficient referred to as “Rayleigh constant”, and CD represents a printed critical dimension. As seen from Equation (1), a reduction in the transferable pattern size is achieved by one of the following ways: shortening the wavelength λ for exposure; increasing the numerical aperture NA; and reducing the value of k1.
In order to shorten the wavelength for exposure and therefore to reduce the transferable pattern size, there has been proposed to use an EUV light generation apparatus that generates EUV light at a wavelength within the range from 10 nm to 20 nm, preferably from 13 nm to 14 nm. As a typical EUV light generation apparatus, there has been known a laser produced plasma (LPP) EUV light generation apparatus, a discharge plasma EUV light generation apparatus, and synchrotron radiated EUV light generation apparatus by using an electron storage ring.
Usually, in the LLP EUV light generation apparatus, Sn droplets are irradiated with a laser beam and turned into plasma, and therefore light at a wavelength within the EUV band is generated. This laser beam may be supplied by, for example, a CO2 laser apparatus.